Joseph LaPorte offers a new account of the connections between the reference of words for properties and kinds, and theoretical identity statements. Some terms for concrete objects, such as "Hesperus" and "Phosphorus," are rigid, and the rigidity of these terms is important because it helps to determine whether certain statements containing them, including identity statements like 'Hesperus = Phosphorus', are necessary or contingent. These observations command broad agreement. But there has been much less agreement about whether and how designators for are rigid: terms like 'white', 'brontosaur', 'beautiful', 'heat', 'H2O', 'pain', and so on. In , LaPorte articulates and defends the position that terms for properties rigid designators. Furthermore, he argues that property designators' rigidity is put to good use in important philosophical arguments supporting and impugning certain theoretical identity statements. The book as a whole constitutes a broad defense of a tradition originating largely in seminal work from Saul Kripke, which affirms the truth and necessity of theoretical identities such as 'water = H2O', 'heat = the motion of molecules' and the like, and which looks skeptically upon psychophysical identities like 'pain = c-fiber firing'. LaPorte responds to detractors of the Kripkean tradition whose objections and challenges indicate where development and clarification is needed, as well as to sympathizers who have put forward important contributions toward such ends. Specific topics discussed by way of defending the Kripkean tradition include conventionalism and empiricism, nominalism about properties, multiple realizability, supervenience, analytic functionalism, conceptual dualism and 'new wave' or a posteriori materialism, the explanatory gap, scientific essentialism (more broadly: scientific necessitarianism), and vitalism.